Powertrain, generic (extended)

P21D7 Cylinder 9 Injector B Circuit/Open

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P21D7 would mark an open drive circuit of the second injector on cylinder 9, which presupposes at least nine cylinders. No manufacturer documents this code publicly; the published Ford and GM lists stop at cylinder 8 (P21D6). Engines with that many cylinders and two injection systems do exist, for example the V10 of the Lamborghini Huracán, which pairs direct with multipoint injection, but no source shows how its maker labels the two injectors. CARB requires that electrical output components such as fuel injectors be checked for circuit faults, so the logic would follow the documented siblings: a missing current or excessive impedance when the injector is switched. The direct injector of cylinder 9 would carry P0209 if it is the A side. A misfire on cylinder 9 (P0309) is the likely accompanying symptom.

Likely causes

Open coil in the second injector of cylinder 9
Broken wire or terminal in the injector harness
Driver stage in the engine control module failed

Symptoms

  • Check engine light on
  • Misfire on cylinder 9 (P0309)

Repair estimate

DifficultyHardWorkshop job
Parts and labour€150–1,000
Time1–5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

fuel injectorinjector wiringengine control module

Related codes

P0209P21ECP21EDP21D6P21D8P0309

References: law.cornell.edu, en.wikipedia.org, fordservicecontent.com.